In an existing wireless communications field, a spectrum resource mainly falls into two types: a licensed spectrum resource and an unlicensed spectrum resource. The licensed spectrum resource is a spectrum resource delimited by a radio regulatory commission of the government for special use, for example, a spectrum resource that is used by a mobile operator or is dedicated for civil aviation, a railway, and police. Due to exclusiveness in terms of policy, quality of service of the licensed spectrum resource may be generally guaranteed, and it is also easier to perform scheduling control on the licensed spectrum resource.
The unlicensed spectrum resource is also a spectrum resource delimited by a related government department. No limitation is imposed on a radio technology, an operation enterprise, or a service life, and quality of service of this frequency band is not guaranteed either. An unlicensed spectrum resource can be free for use, provided that a communications device that uses the unlicensed spectrum resource meets a requirement on a transmit power indicator, an out-of-band leakage indicator, or another indicator. A common communications system in which the unlicensed spectrum resource is used for communication includes a civil walkie-talkie, a radio remote controller, a Wireless Fidelity (Wi-Fi) communications system, a Bluetooth communications system, or the like.
In an existing Long Term Evolution (LTE) system, a spectrum resource used by an operator is mainly a licensed spectrum resource. With a growing quantity of users in a mobile communications network and a higher user requirement on a communication speed and quality of service, it is difficult to meet the operator's demand for an existing service by using the existing licensed spectrum resource. Considering that a new licensed spectrum is expensive and is scarce, the operator starts to pay attention to an unlicensed spectrum resource, to hope that the unlicensed spectrum resource can be used to implement network capacity offloading and quality of service improvement. A licensed-assisted access using Long Term Evolution (LAA-LTE) system or a Long Term Evolution in unlicensed spectrum (U-LTE) system is used to study an issue that the unlicensed spectrum resource is applied to the LTE system for communication.
To ensure friendly coexistence of a system and a device that communicate in an unlicensed spectrum, a listen-before-talk (LBT) channel access mechanism is introduced in some countries and regions, for example, Europe and Japan. A basic concept of LBT is as follows: Before sending a signal on a channel, each communications device needs to first detect whether the current channel is idle, that is, whether it can be detected that a neighboring node is occupying the channel for sending a signal. This detection process is referred to as clear channel assessment (CCA). If it is detected, within a time period, that the channel is idle, the communications device may send the signal. If it is detected that the channel is occupied, the communications device cannot send a signal currently. Specifically, as specified by European regulations, the LBT mechanism is further classified into a frame based equipment (FBE) LBT mechanism and a load based equipment (LBE) LBT mechanism. A channel access manner in a Wi-Fi system is one type of LBE, and is specifically a carrier sense multiple access with collision avoidance CSMA/CA for short) mechanism. In the LBE access mechanism specified by the regulations, when system detection indicates collision, a contention window is a fixed value. However, in the LBE channel access mechanism of the Wi-Fi, when system detection indicates collision, a contention window exponentially increases. If the LAA system meets only a requirement made by the regulations, when the LAA system and the Wi-Fi system contend for a channel, once resource collision occurs, there is a higher probability that a channel may be preempted in the LAA. Consequently, a probability that the channel is accessed in the Wi-Fi system is reduced, and fair coexistence with the Wi-Fi cannot be ensured.